Method of chemical vapor deposition

ABSTRACT

A method of performing chemical vapor deposition which produces semiconductor crystalline thin films having small transition widths. The method involves the use of a cold-wall type reaction chamber that is equipped with a gas inlet at one end and a gas outlet at the other end and a semiconductor substrate support which supports a semiconductor substrate so that a main surface thereof is horizontal. A reactant gas is caused to flow horizontally through the reaction chamber to effect the growing of a crystalline thin film on the main surface of the semiconductor substrate. The semiconductor substrate is arranged within the reactor chamber within a distance W which is measured from a leading edge of the semiconductor substrate at a most upstream position along a direction toward the gas outlet where W indicates an internal width of the reaction chamber. The semiconductor substrate is also in a location having a W/G ratio of 15 or greater, where G represents a distance between the main surface of the semiconductor substrate and a ceiling of the reaction chamber.

This is a Divisional of application Ser. No. 09/007,012, filed Jan. 14,1998, now abandoned which is a Continuation Application of applicationSer. No. 08/502,042 filed Jul. 13, 1995 now U.S. Pat. No. 5,749,974.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of a chemical vapordeposition, where a reactant raw material gas(es) is transported onto asemiconductor crystalline substrate(s) to grow a semiconductorcrystalline thin film(s) thereon, and to a reactor therefor.

2. Description of the Prior Art

A horizontal chemical vapor deposition reactor, as shown conceptually ina simplified form in FIG. 6 is comprised of a cold-wall type reactionchamber 3 being composed of a gas inlet 5 for a reactant raw materialgas(es) 4 at one end and a gas outlet 6 at the other end being alignedhorizontally and holding a semiconductor crystalline substrate(s) 1(hereafter simply referred to as a substrate) roughly horizontally inthe chamber 3, and grows a desired semiconductor thin film(s) 2 on thesubstrate(s) 1, while the substrate(s) 1 is heated and the reactant rawmaterial gas(es) 4 is flown through the substrate(s) 1 in one directionin the reaction chamber 3.

In a horizontal reactor for a chemical vapor deposition of the priorart, as shown conceptually in a simplified form as well in FIG. 7, whichis a front view of the chamber 3 in section shown in FIG. 6 as seen fromthe side of the gas inlet 5, the internal height H of the chamber 3 isso determined as to accommodate a susceptor (not shown) laid on thebottom of the reaction chamber 3 on which a substrate(s) 1 is held and amechanical driving device for a substrate transportation (both notshown).

With respect to the internal width W of the chamber 3 as shown in FIG. 7it is so determined that a proper gap is added to a diameter of asusceptor (not shown) or a diameter D of a substrate(s) 1 thereon forreceiving or drawing out.

In a chemical vapor deposition using a traditional type of the reactionchamber 3 designed in. such a manner as described above, when, inparticular, a low impurity content semiconductor thin film(s) 2 is grownon a substrate(s) 1 having a high impurity content whose concentrationis higher than that of the thin film(s) 2 by at least two figures, atransition width T located at the interface between the substrate 1 andthe semiconductor thin film 2, where the impurity level in thesemiconductor thin film 2 changes gradually from the concentration ofthe substrate 1 to a desired concentration, is unfavorably spread andthus many trials have been carried out to reduce the transition width T.

To find a better condition for minimizing the transition width T, therehave to be done a study about the causes of the transition width T.Traditionally two causes have been raised for the formation of thetransition width T, which are out-diffusion O in a solid and autodopingA.

The out-diffusion O in a solid is a phenomenon that an impurity diffusesinto a semiconductor thin film 2 from a substrate 1 depending on agrowth temperature of the semiconductor thin film 2.

This phenomenon is always dependent on impurity concentration, heatingtemperature and heating time.

To diminish the phenomenon, one of two ways is chosen, either loweringtemperature or shortening heating time.

However, when the heating temperature is lowered in order to suppressthe out-diffusion O, automatically affecting to the growth rate to belowered by itself, the growth rate is required to be reduced further toprevent the surface appearance of a crystalline thin film fromroughening.

Under the conditions, the growth time (in other words, the heating timeextended to attain a desired thickness of the film) causes not only theenhancement of the out-diffusion in a solid, which reduces thesuppression effect of the out-diffusion, but also the reduction of theproduction efficiency.

On the other hand, the autodoping A is a phenomenon that an impuritymoved out from the substrate 1 into the gas phase therearound isincorporated back into the growing surface of a semiconductorcrystalline thin film 2.

This phenomenon is also able to be suppressed by either lowering heatingtemperature or by shortening heating time.

But, both of the means are not better ways to be adopted, because assame as the case of the out-diffusion O mentioned above, both of themeans give only small suppression effect to the autodoping A, and alsocause a decrease of the production efficiency by lowering the growthrate.

In company with the recent general trend of increasingly higherintegrated electronic devices using the semiconductor single crystallinethin films produced by a gas phase epitaxial deposition, much thinnersemiconductor crystalline film has been required, and more recently,there has arose a new requirement that the film thickness is equal to orthinner than the transition width T of generally available in the past.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of achemical vapor deposition and a reactor therefor, whereby asemiconductor crystalline film having a transition width smaller thanthat grown by the traditional chemical vapor deposition technique isobtained in the same reaction condition.

The present invention is directed to a method of chemical vapordeposition which is conducted in a cold-wall type reaction chamber thatis equipped with a gas inlet for a reactant raw material gas(es) at oneend and a gas outlet for a reaction gas at the other end, installed inroughly horizontal, holding a semiconductor substrate(s) in the chamberwith a main surface of the substrate aligned in roughly horizontal,flowing a reactant raw material gas(es) in roughly horizontal in onedirection, and growing a desired semiconductor crystalline thin film(s)on the heated semiconductor substrate(s),

characterized in that the substrate(s) is arranged in a range of (L+W)from the gas inlet of the reactant raw material gas(es) in the flowingdirection and in a location of W/G ratio is 15 or larger, where Windicates an internal width of the reaction chamber, L indicates adistance from the gas inlet of the reactant raw material gas(es) to theleading edge of the substrate located at the most upstream position onthe inlet side and G indicates the distance between the main surface ofthe substrate and a ceiling thereabove.

The present invention is further directed to a method of chemical vapordeposition which is characterized in that the semiconductor substrate(s)is so selected that the diameter thereof is less than the internal widthW of the reaction chamber.

The present invention is further directed to a method of chemical vapordeposition which is characterized in that each of the gaps between thesemiconductor substrate(s) and the internal side walls is so selected asto be 3 cm or wider.

A reactor for a chemical vapor deposition according to the presentinvention comprises of a cold-wall type reaction chamber that isequipped with a gas inlet for a reactant raw material gas(es) at one endand a gas outlet for a reaction gas at the other end, installed inroughly horizontal, and a supporting means for a semiconductorsubstrate(s) being held in the chamber with a main surface of thesubstrate aligned in roughly horizontal, flowing a reactant raw materialgas(es) in roughly horizontal in one direction, and growing a desiredsemiconductor crystalline thin film(s) on the heated semiconductorsubstrate(s),

characterized in that the supporting means for the substrate(s) isarranged in a range of (L+W) from the gas inlet of the reactant rawmaterial gas(es) in the flowing direction and in a location of W/G ratiois 15 or larger, where W indicates an internal width of the reactionchamber, L indicates a distance from the gas inlet of the reactant rawmaterial gas(es) to the leading edge of the substrate located at themost upstream position on the gas inlet side and G indicates thedistance between the main surface of the substrate and a ceilingthereabove.

The present invention is further directed to a reactor for chemicalvapor deposition which is comprised of a cold-wall type reaction chamberthat is equipped with a gas inlet for a reactant raw material gas(es) atone end and a gas outlet for a reaction gas at the other end, installedin roughly horizontal, and a supporting means for a semiconductorsubstrate(s) being held in the chamber with a main surface of thesubstrate aligned in roughly horizontal, flowing a reactant raw materialgas(es) in roughly horizontal in one direction, and growing a desiredsemiconductor crystalline thin film(s) on the heated semiconductorsubstrate(s),

characterized in that the dimensions of the reaction chamber are soselected that the internal length thereof in the flowing direction ofthe reactant raw material gas(es) is longer than (L+W) and W/H ratio is15 or larger, where W indicates an internal width of the reactionchamber, H indicates an internal height of the chamber, L indicates adistance from the gas inlet of the reactant raw material gas(es) to theleading edge of the substrate located at the most upstream position onthe gas inlet side.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and objects of the present invention will become apparentfrom a study of the following description of a method of a chemicalvapor deposition and a reactor therefor, whereby a semiconductorcrystalline film having a transition width smaller than that to beobtained by the traditional chemical vapor deposition technique in thesame reaction conditions, together with the accompanying drawings, ofwhich:

FIG. 1 is conceptual representations of a main part in a reactor for achemical vapor deposition according to a first embodiment of the presentinvention and, in particular, FIG. 1(a) is a perspective view of areaction chamber, FIG. 1(b) is a top plane view thereof and FIG. 1 (c)is a vertical sectional view thereof;

FIG. 2 is a graph showing experimental results of vapor phase epitaxialgrowths conducted in a first embodiment about a relation between W/Gratio in a reaction chamber and rotation number of a vertical vortexthat is generated by a natural convection during a passage of a reactantraw material gas(es) over a heated region;

FIG. 3 is another graph showing experimental results of vapor phaseepitaxial growths conducted in a first embodiment about a relationbetween W/G ratio in a reaction chamber and transition region width of asemiconductor crystalline thin film;

FIG. 4 is a schematic sectional view of a reaction chamber in a secondembodiment;

FIG. 5 is an impurity concentration profile in the thickness direction;

FIG. 6 is a perspective view illustrating a stream pattern of a naturalconvection of a reactant raw material gas(es) generated in a traditionalhorizontal type reactor for a chemical vapor deposition;

FIG. 7 is a sectional plane view of FIG. 6 illustrating a stream patternof vertical vortexes of reactant raw material gases generated in thereaction chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will be calculative and preliminary experimental results describedconcerning about the autodoping phenomenon.

The inventors have investigated about the autodoping phenomenon, whichis one of the causes of increasing a transition width, by using ahorizontal type reactor for a chemical vapor deposition.

The details of the investigation are as follows: In a cold-wall typereaction chamber aligned almost in horizontal holding a substrate(s)therein, when a reactant raw material gas(es) is led into the chamberbeing flown over the substrate almost in horizontal and in onedirection, while heating the substrate for growing a crystalline thinfilm thereon, vortexes due to natural convection generated by atemperature difference between the reaction chamber and the heated areacarry an impurity which was moved out from the substrate, in particular,from the backside thereof and then return the impurity to theneighboring point of the substrate in each time when the vortexes havechances to be incorporated with the growing surface of the crystallinethin film.

The inventors have found that the vortexes carrying a impurity from thesubstrate are one of the causes of the autodoping phenomenon.

In a traditional type of a horizontal reactor for a chemical vapordeposition as shown in FIGS. 6 and 7, which has a large space above asubstrate 1 in the reaction chamber 3, large vertical vortexes 12 due tonatural convection 11 are generated in such a manner that a part of thereactant raw material gas 4 is being moved upward above the centralregion of the heated substrate 1 and moved downward in the vicinity ofthe cooled side walls 7 of the chamber 3 as the reactant raw materialgas 4 is flowing inside the chamber 3 toward the downstream.

By a theoretical analysis through calculations using Grashof number andRayleigh number as parameters on the basis of the hydrodynamics, ageneration frequency of the vertical vortexes 12 due to naturalconvection 11 is found proportional to the third power of the internalheight H of the reaction chamber 3 on an assumed condition that thesubstrate 1 is held directly on the internal bottom surface of thereaction chamber 3.

When a space above the substrate 1 is wider, the impurity in the naturalconvection originated from the substrate 1 increases the probability tobe incorporated with the substrate 1, resulting larger autodoping andwider transition width.

In a horizontal type reactor for a chemical vapor deposition comprisinga cold wall type reaction chamber, a series of experiments to growsemiconductor crystalline thin films 2 have been carried out bynarrowing the distance G between the main surface of a substrate 1 andthe ceiling of the reaction chamber 3 gradually for measuring eachtransition width at each distance G, and at the same time, rotationnumber of a vortex 12 under each condition was estimated by calculationsand gas flow visualization experiments.

Both of the rotation number of the vortex and the transition width werestudied on the relations with W/G ratio, where W/G ratio indicates theratio of the internal width W of the reaction chamber 3 to the distanceG between the main surface of the substrate 1 and the ceilingthereabove.

One of the results of the study showed that in the case when an internalwidth W of a reaction chamber 3 was 40 cm, a distance G of 2 cm betweena main surface of a substrate 1 and the ceiling thereabove, that is, W/Gratio was 20, the rotation number of the vortex 12 due to naturalconvection 11 generated above the substrate 1 in the passage of amixture of raw material gases 4 over a heated region, whose diameter was30 cm, was suppressed to about 0.5 rotations.

In FIGS. 6 and 7, the internal width W is a distance between the bothinternal walls 7, 7 of the reaction chamber 3.

A study covering several experiments showed that in the case when W/Gratio was 15 or larger, the rotation number of the vertical vortex 12was suppressed to 1 or less within the distance of (L+W) in the flowingdirection of the raw material gases 4 and therefore the autodopingphenomenon was reduced to be as small as negligible, where L indicates adistance from the gas inlet 5 for the reactant raw material gases 4 tothe leading edge of the substrate 1 located at the most upstreamposition on the inlet side.

When W/H ratio is selected at 15 or larger, since the substrate 1 isheld in the reaction chamber 3, W/G ratio is automatically regulated to15 or larger, where H indicates the internal height of the reactionchamber 3 at the position where the substrate 1 is held.

As mentioned above, when W/G ratio or W/H ratio is selected to be 15 orlarger and the distance G between the main surface of the substrate 1and the ceiling thereabove is reduced, the rotation number of a verticalvortex 12 due to natural convection 11 is suppressed above a heatedregion within the distance of (L+W) from the gas inlet 5 in the flowingdirection of the reactant raw material gases 4, resulting in the factsthat the autodoping phenomenon is suppressed to be as small asnegligible and thereby the transition width T is decreased.

On the other hand, a stagnant layer of the reactant raw material gases 4is formed in the vicinity of all the sidewalls 7, 7 of the reactionchamber 3, where the flow rate is very low.

The thickness of the stagnant layer is found to be 3 cm at the highestand has no relation to the internal width W of the reaction chamber 3 orthe diameter D of the substrate 1 held inside the chamber 3.

When an impurity migrates from a substrate 1, in particular from theback surface thereof, into the stagnant layer, the probability ofautodoping is high because the impurity stays long in the stagnant layerwhere the flow rate is low.

Consequently, when a chemical vapor deposition is carried out in thecondition that both of the outer sides of the substrate 1 are separatedfrom the internal walls 7, 7 by 3 cm or wider in length respectively,since any part of the substrate 1 is not located within the stagnantlayer site, none of the autodoping originated from the stagnant layer isgenerated, so that the entire substrate 1 is kept the same environmentalcondition with respect to the flow of the reactant raw material gases 4.

Next, detail embodiments of the reactor operated under normalatmospheric pressure according to the present invention will beexplained in reference to the accompanying drawings.

Embodiment 1.

FIG. 1 is conceptual representations of a main part in a reactor for achemical vapor deposition according to a first embodiment of the presentinvention and, in particular, FIG. 1(a) is a perspective view of areaction chamber 3, FIG. 1(b) is a top plane view thereof and FIG. 1(c)is a vertical sectional view thereof.

A substrate 1 is placed in a reaction chamber 3 and a mixture ofreactant raw material gases 4 flows over the substrate I heated at adesired temperature to grow a semiconductor crystalline thin film 2 onthe substrate 1. There are several methods to heat up the substrate 1 toa desired temperature, such as, a method to provide a radiation energylike infrared rays to the substrate 1 through reaction chamber walls, amethod to have a resistance heater inserted beneath the substrate 1 andheated by electricity, a method to have a induction heater beneath thesubstrate 1.

When a semiconductor, such as, a silicon crystalline thin film 2 isgrown by a chemical vapor deposition, walls 7, 7 of the reaction chamber3 are kept at a low temperature in order that semiconductor crystal doesnot deposit on the internal surfaces of the walls, while the substrate 1is heated.

Under such a reaction environment, only the substrate 1 is heated to ahigh temperature, while the area around the substrate 1 remains at atemperature a little higher than room temperature.

A chamber that produces such a temperature environment around thesubstrate 1 is generally called as a cold-type chamber.

Natural convection 11 is apt to occur inside the cold-type chamber dueto the great temperature difference between a substrate 1 and the wallsof a reaction chamber 3.

A series of silicon single crystalline thin films were grown on siliconcrystalline substrates in the first embodiment of the reactor for achemical vapor deposition of the present invention and the results weredescribed below in detail.

A silicon single crystalline substrate 1, which had a conductance ofp-type, a resistivity of about 0.02 ohm.cm and a diameter D of 20 cm,was placed on a susceptor, not shown, in the reaction chamber 3 andheated up to 1100° C., where the susceptor has a diameter of a littlesmaller than the internal width of the reaction chamber 3.

The configuration of the reaction chamber 3 for a chemical vapordeposition in the first embodiment was set as follows; the distance Lfrom a gas inlet 5 for a mixture of reactant raw material gases 4 to theleading edge of the substrate 1 was 20 cm, the gap d1, d2 between theinternal side walls 7, 7 of the reaction chamber 3 and the nearestportions of the outer edge of the substrate 1 was 5 cm each, theinternal width W of the chamber 3 was 30 cm, the distance G between themain surface of the substrate 1 and the ceiling of the chamberthereabove was so selected as to change gradually in the range of 1.5 cmto 6 cm, which means W/G ratio was in a range of 5 to 20.

A series of vapor phase epitaxial growths were conducted under thefollowing conditions.

A mixture of reactant raw material gases 4 was prepared by mixing 3.6l/min. of trichlorosilane gas with hydrogen gas and the mixture wassupplied horizontally into the reaction chamber 3 in one direction at aflow rate of 100 /min. through the gas inlet 5 of the reaction chamber3.

In this condition, the rotation number of each of vortexes wasdetermined by calculations on the basis of hydrodynamics andvisualization experiments so as to study a relation between the rotationnumber and W/G ratio, where the vortexes were generated due to naturalconvection of reactant raw material gases 4 on the susceptor as a heatedregion, while the mixture of raw material gases 4 flowed above thesubstrate.

As dearly shown in FIG. 2 it was found that the rotation number N of thevertical vortexes 12 became 1 rotation or less when W/G ratio was 15 orlarger.

This means that a condition is achievable in which an impurity moved outfrom the very leading edge of the substrate 1 into the surrounding gasphase does not incorporate back into the single crystalline thin film 2.

Then, to verify the practical effect of aforementioned conditions, aseries of silicon single crystalline thin films 2 were grown to measurea transition width for each condition.

The growth conditions were essentially the same as those of theaforementioned experiments on the investigation about the verticalvortexes 12.

In theses experiments, substrates 1 were exposed in a hydrogenatmosphere at 1190° C. for 90 seconds in order to dean the surfaces ofthe substrates 1 prior to the growth of the silicon single crystallinefilms 2.

A period of time when a trichlorosilane mixed reaction gas is introducedinto a reaction chamber 3 to grow a silicon single crystalline thin film2 was set to be 1 min.

Diborane as a dopant gas was mixed into the reactant raw material gas sothat the resistivity of the silicon single crystalline thin film 2 iscontrolled to be 10 ohm.cm in p-type.

In the above growth conditions, each of the silicon single crystallinethin films 2 grown to be about 3 μm in thickness was measured by asecondary ion mass spectroscopy (SIMS) to investigate dopantconcentration profile in the silicon single crystalline thin films 2formed on the substrates 1.

A relation between the transition width and W/G ratio was shown in FIG.3.

It was found from the FIG. 3 that the transition width was changed in acorrelating manner to the change of W/G ratio, even if the condition ofthe reactant raw material gas was kept the same, and the transitionwidth was not lowered to a value of less than 0.5 μm.

The lowest value of the transition width was determined by anout-diffusion in a solid occurred during the pretreatment for cleaning asurface of a substrate 1 and the following growth of a semiconductorcrystalline thin film 2.

That is, it was found that a silicon single crystalline thin film 2, inwhich the influence of autodoping was suppressed as small as negligibleand the transition width was small as the result could be grown, when aW/G ratio was selected to be 15 or larger.

Embodiment 2

FIG. 4 is a schematic sectional view of the reaction chamber 3 in thereactor of a second embodiment.

The reaction chamber 3 has a recess at a part of the bottom and asusceptor 9 is located in the recess 8.

The W/G ratio is selected to be 15 or larger, where G indicates thedistance from the main surface of a substrate 1 held on the susceptor 9to the ceiling thereabove.

In the reaction chamber 3, because a main surface of a substrate 1 isleveled with the internal bottom surface other than the recess 8, whenthe substrate 1 is placed on the susceptor 9, a mixture of raw materialgases 4 flows smoothly without any obstruction to the flow at theleading edge of the substrate 1 as well as at the leading edge of thesusceptor 9, so that a disturbance in the stream of the mixture of rawmaterial gases 4 becomes scarce to occur and thus the objects of thepresent invention can be achieved for certain.

On the other hand, it may be possible to suppress a natural convectionoccurring between the main surface of a substrate and the ceilingthereabove by the effect of an increased flow rate of a gas.

But an extremely large flow rate is required in order to effectivelyminimize the influence of autodoping.

That is to say, to try to minimize a transition width by an increasedgas flow rate is never a recommendable way from a view point of theproduction cost of a wafer with a chemical vapor deposition thin filmthereon.

The detailed description was made in the embodiments 1 and 2 about avapor phase epitaxial growth conducted to grow a silicon singlecrystalline thin film on a silicon single crystalline substrate.

The present invention is, however, not limited to the embodiments aboveand it is needless to say that a variety of modifications can be made inother embodiments still within the scope of the present invention.

For example, a single substrate is used for explaining the aboveembodiments 1 and 2, but the present invention can naturally beapplicable to the cases where a plurality of substrates are held in areaction chamber only if they are located within an interval of (L+W)from the gas inlet of a reactant raw material gas(es) in the gas flowingdirection.

The present invention is also effective to grow a polycrystalline thinfilm on a substrate by a chemical vapor deposition.

In the method of a chemical vapor deposition and a reactor thereforaccording to the present invention, as is made clear from theexplanation above, a space above a substrate held in the reactionchamber is designed to be small and the location of a substrate(s) isarranged within a certain interval in the reaction chamber, and thus theoccurrence of natural convection in the space is suppressed.

The suppression effect of natural convection in the space is effectiveto minimize autodoping caused by an impurity coming out from such as aback surface of a substrate during a chemical vapor deposition and thusthe transition width on a substrate is uniformly suppressed across theentire surface of the substrate.

What is claimed is:
 1. A method of performing chemical vapor depositionwhich comprises: providing a horizontal cold-wall reaction chamberequipped with a gas inlet at an upstream end for receiving a reactantgas, and a gas outlet at a downstream end for flowing a reactant gashorizontally in one direction through said reaction chamber; supportinga semiconductor substrate in the reaction chamber so that a main surfaceof the semiconductor substrate is aligned horizontally; arranging thesemiconductor substrate within a distance W measured from a leading edgeof the semiconductor substrate, which leading edge is located at a mostupstream portion of the reaction chamber, along a direction toward thegas outlet, and the semiconductor substrate being positioned in alocation in which a W/G ratio is 15 or larger so that a rotation numberof a vertical vortex due to natural convection is suppressed to 1 orless within the distance W measured from a leading edge of thesemiconductor substrate, wherein W is an internal width of the reactionchamber and G is a distance between the main surface of thesemiconductor substrate and a ceiling of the reaction chamber above thesemiconductor substrate; heating the semiconductor substrate to atemperature for growing a crystalline film on the semiconductorsubstrate, said temperature being sufficient to create naturalconvection between the semiconductor substrate and internal side wallsof the reaction chamber due to temperature differences therebetween; andsuppying the reaction chamber with a reactant gas; and growing acrystalline film on the semiconductor substrate by chemical vapordeposition.
 2. A method of performing chemical vapor deposition asdefined in claim 1, wherein the semiconductor substrate is selected soas to have a diameter which is less than the internal width W of thereaction chamber.
 3. A method of performing chemical vapor depositionaccording to claim 2, further comprising supporting the semiconductorsubstrate in the reaction chamber so that the semiconductor substrate isat least 3 cm from internal side walls of the reaction chamber.
 4. Amethod of performing chemical vapor deposition according to claim 1,further comprising supporting the semiconductor substrate in thereaction chamber so that the semiconductor substrate is at least 3 cmfrom internal side walls of the reaction chamber.
 5. A method ofperforming chemical vapor deposition according to claim 1, furthercomprising providing a reactant gas to the inlet which produces asilicon crystalline thin film on the semiconductor substrate.
 6. Amethod of performing chemical vapor deposition which comprises:providing a horizontal cold-wall reaction chamber equipped with a gasinlet at an upstream end for receiving a reactant gas, and a gas outletat a downstream end for flowing a reactant gas horizontally in onedirection through said reaction chamber; supporting a semiconductorsubstrate in the reaction chamber so that a main surface of thesemiconductor substrate is aligned horizontally; heating thesemiconductor substrate to a temperature for growing a crystalline filmon the semiconductor substrate, said temperature being sufficient tocreate natural convection between the semiconductor substrate andinternal side walls of the reaction chamber due to temperaturedifferences therebetween; providing the reaction chamber with aninternal length as measured along a direction which extends between thegas inlet and the gas outlet that is greater than W, and a W/H ratio of15 or larger, so that a rotation number of a vertical vortex due tonatural convection is suppressed to 1 or less within the distance Wmeasured from a leading edge of the semiconductor substrate, wherein Wis an internal width of the reaction chamber and H is an internal heightof the reaction chamber; supplying the reaction chamber with a reactantgas; and growing a crystalline film on the semiconductor substrate bychemical vapor deposition.
 7. A method of performing chemical vapordeposition reactor according to claim 6, further comprising supportingthe semiconductor substrate in the reaction chamber so that thesemiconductor substrate is at least 3 cm from internal side walls of thereaction chamber.
 8. A method of performing chemical vapor depositionaccording to claim 6, further comprising providing a reactant gas to theinlet which produces a silicon crystalline thin film on thesemiconductor substrate.
 9. A method of performing chemical vapordeposition as defined in claim 6, wherein the semiconductor substrate isselected so as to have a diameter which is less than the internal widthW of the reaction chamber.
 10. A method of performing chemical vapordeposition according to claim 9, further comprising supporting thesemiconductor substrate in the reaction chamber so that thesemiconductor substrate is at least 3 cm from internal side walls of thereaction chamber.